Sex allocation in a polygynous mammal with large litters: the wild boar

Predictions from Trivers & Willard's (1973, Science, 179, 90–92) hypothesis of sex-biased maternal investment in polygynous species do not apply well to species where mothers produce more than one offspring per reproductive attempt. First, as litter size increases, the benefits to the mothe...

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Bibliographic Details
Published in:Animal behaviour 1999-11, Vol.58 (5), p.1079-1084
Main Authors: FernáNdez-Llario, Pedro, Carranza, Juan, Mateos-Quesada, Patricio
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal behavior
Animal reproduction
Animal, plant and microbial ecology
Animals
Autoecology
Biological and medical sciences
Fundamental and applied biological sciences. Psychology
Mammalia
Mammals
Spain
Sus scrofa
Vertebrata
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Summary:Predictions from Trivers & Willard's (1973, Science, 179, 90–92) hypothesis of sex-biased maternal investment in polygynous species do not apply well to species where mothers produce more than one offspring per reproductive attempt. First, as litter size increases, the benefits to the mother of adjusting sex ratio decrease because (1) she could benefit more by adjusting litter size and (2) sex differences in reproductive potential are negatively related to litter size. Second, testing sex-biased investment in these species requires predictions about the simultaneous adjustment of sex ratio and litter size. The wild boar, Sus scrofa, although polygynous, produces large litters. Here we present data for 58 litters from a free-ranging wild boar population in central Spain. Maternal expenditure per individual offspring, as measured by piglet weight, was higher for male than female fetuses. In more than 81% of cases the heaviest fetus in the litter was a male regardless of the quality of the mother; this might have influenced his ranking within the ‘teat order’ and consequently his development and survival. Mother quality (size and weight) appeared to be related to litter size but not to the sex ratio of the litter. However, it was highly related to a variable that combined the effects of litter size and sex ratio within the litter, thus supporting Williams' (1979, Proceedings of the Royal Society of London, Series B, 205, 567–580) hypothesis that mothers should adjust both litter size and offspring sex.
ISSN:0003-3472
1095-8282
DOI:10.1006/anbe.1999.1234